PVS-Studio warning V595 for Doom3

void idBrushBSP::FloodThroughPortals_r(idBrushBSPNode *node, ...)
{
  ...
  if ( node->occupied ) {
    common->Error(
      "FloodThroughPortals_r: node already occupied\n" );
  }
  if ( !node ) {
    common->Error(
      "FloodThroughPortals_r: NULL node\n" );
  }
  ...
}

This is what should have been written here: if ( node && node->occupied ) {

This suspicious code was found in Doom3 project by PVS-Studio static code analyzer.
Warning message is:
V595 The 'node' pointer was utilized before it was verified against nullptr. Check lines: 1421, 1424. DoomDLL brushbsp.cpp 1421

PVS-Studio is a static analyzer for detecting bugs in the source code of applications written in C, C++, C++11, C++/CX. Site: http://www.viva64.com/en/pvs-studio/